In a field of a semiconductor device, a magnetic material device, and a superconductor device, degree of integration has been becoming higher and higher, fine patterns each having a size of no greater than 1 .mu.m are about to be mass-produced. Feeding an ultra-high purity gas is indispensable for forming fine patterns as described above, at present, and efforts has been made so that a density of impurity in the gas can be suppressed to not more than a couple of ppb, and furthermore to a couple of ppt.
On the other hand, a halogen-based corrosive gas represented by HBr and HCl or the like is often used, for instance, as a process gas for etching in semiconductor production. For this reason, a gas contact section has to be excellent also in corrosion resistance to prevent generation of any corrosive products due to contact with the gas.
The inventor has developed several types of the technology to satisfy the needs as described above, and one of them is the technology for forming a passivated film characterized in that a denatured layer which is formed by microcrystallization is formed on the surface of a stainless steel base material by means of composite electrolytic polishing, then, the surface is baked in an inert gas so as to remove moisture from the surface of the stainless steel, and then heat-treatment is carried out in temperature range from 450.degree. C. to 600.degree. C. in a mixed gas atmosphere of an inert gas and 500 ppb to 2% of H.sub.2 O gas (Japanese Patent Application No. 266382/1992).
With this technology, it is possible to form an oxide-passivated film having a layer made of amorphous chromium oxide with a thickness of not less than 20 nm on the outermost surface. The stainless steel on which the passivated film is formed has a surface which not only shows excellent corrosion resistance to a highly corrosive gas, but also which a quantity of impurities containing mainly moisture and hydrocarbon deposited thereto is quite small, and even if some of the impurities is deposited thereto, the impurities can be removed from the surface with low energy. Furthermore, the surface is an extremely chemically stable one which does not show any catalytic effect to an active gas made of special ingredients such as SiH.sub.4, B.sub.2 H.sub.6. As a result, in a gas feed system in which piping is formed with the stainless steel, a gas in which a density of impurity is suppressed to a level of a couple of ppt can be fed to a process chamber.
However, the technology described above is generally used mainly for an austenite system SUS316L.
The surface of this passivated film not only has excellent corrosion resistance to the highly corrosive gas as described above, but also a quantity of impurities containing mainly moisture and hydrocarbon deposited thereon is quite small, and even if some of impurities are deposited thereon, the impurities can be removed therefrom with low energy. Furthermore, the surface is an extremely chemically stable one which does not show any catalytic effect to an active gas made of special ingredients such as SiH.sub.4, B.sub.2 H.sub.6.
By the way, in the technology for forming a passivated film, it is essential to form a fine denatured layer by using the technology of composite electrolytic polishing, buffing, or polishing with abrasive grains before heat-treatment is carried out to form the passivated film.
However, when composite electrolytic polishing is conducted on, for instance, the internal surface of a 1/4-inch type of tubing, it is not always easy to conduct the polishing uniformly to the tubing, so that in some cases, the fine deformed layer may not be formed on some portions. For this reason, the passivated film having a layer made of chromium oxide can not be formed on the outermost surface of the portions even if heat-treatment for forming a passivated film is carried out. Also, workmanship in composite electrolytic polishing is difficult as compared to that in electrolytic polishing, so that experience is required.
An object of the present invention is to provide a method of forming a passivated film capable of forming an oxide-passivated film having a layer made of chromium oxide on the outermost surface without conducting composite electrolytic polishing.
Another object of the present invention is to provide an ultra-high purity fluid feed system, a process apparatus, and a fluid contact component, each of which uses steel having materials for ferrite-based stainless steel completely controlled, is free from metal contamination, and has excellent discharge gas characteristics, non-catalytic property, and high corrosion resistance.